A stenosis in a blood vessel obstructing blood flow through a patient's body may cause severe health problems to the patient. Medical treatment, catheter intervention, or even surgery might be necessary if severity of the stenosis is high and/or if the stenosis is at a particularly hazardous location. Therefore it is of high importance that a physician has sufficient and reliable data available about the stenosis location and severity.
Degree of stenosis is the most used parameter for diagnosis. Hemodynamic severity of the stenosis may be functionally assessed by evaluating in-artery (catheterized) pressure or flow measurements, from which fractional flow reserve (FFR), pressure drop or stenotic resistance can be determined. This invasive procedure requires precise and time consuming procedural work, costly catheters, as well as interventional risks since the stenosis needs to be passed with the catheter. As an alternative, non-invasive measurements using radiation imaging are known, e.g. using x-ray radiation imaging, such as, for example, computed tomography (CT) imaging (see FIG. 1a), 2D x-ray angiography or (rotational) C-arm x-ray imaging (see FIG. 1b). With these techniques images of a part of the body comprising the stenosed artery are generated. Through computational models, such as computational fluid dynamics (CFD) simulations the FFR can be simulated for various locations in the stenosed artery, for instance as disclosed in U.S. Pat. No. 8,321,150 B2. Other functional parameters as the stenotic resistance or virtual functional assessment indices can also be calculated based on CFD models, such as for instance disclosed in Michail I. Papafaklis et. al., ‘Fast virtual functional assessment of intermediate coronary lesions using routine angiographic data and blood flow simulation in humans: comparison with pressure wire—fractional flow reserve’, EuroIntervention 2014; July 2014.
CFD simulation uses a 3D segmentation obtained from CT or x-ray images and specific boundary conditions at the inlets (e.g. at or after the aorta) and outlets (e.g. at the drains to micro-vasculature). The boundary conditions are typically estimated from scaling laws, systemic parameters like the blood pressure measured at the extremities or an amount of muscle/tissue receiving the arterial blood flow. As the simulated FFR is sensitive to these boundary conditions, this approach may be unreliable in some cases.
Also boundary conditions are, in known CFD models, usually estimated from previous pressure/flow measurements or CFD simulations of the same, or even a different, patient. These may however significantly deviate from an actual situation in the patient currently under examination. First, conditions may change per patient and over time. For instance, local geometries within the vascular system may be vastly different between different patients or may have changed over time within the same patient, possibly even (partly) due to the presence of the stenosis. Also, the conditions may have been determined at different moments in the cardiac cycle and/or there might have been a difference in the frequency, strength, etc. of the cardiac cycle itself may be different.